ISO 1478 Tapping Screw Thread
ISO 1478 specifies the thread requirements for tapping screws, including thread dimensions and profile characteristics for different nominal sizes. These requirements help ensure consistent thread geometry and compatibility with the intended applications. The standard covers tapping screw thread sizes from ST2.2 to ST9.5, providing a common reference for product design, manufacturing, and inspection.
ISO 1478 focuses on the thread itself rather than the complete screw design. Head dimensions, drive types, and other product-specific features are covered by the relevant tapping screw product standards, such as ISO 7049 for cross-recessed pan head tapping screws and ISO 7050 for cross-recessed countersunk head tapping screws. Together, these standards help manufacturers and buyers identify the appropriate specifications for different tapping screw designs.
Thread End Type:
ISO 1478 defines different thread end types for tapping screws, including cone ends, flat ends, and rounded ends. Each design features a different tip geometry that affects how the screw engages with the workpiece during installation. Cone ends provide a tapered tip, flat ends have a flat terminal surface, and rounded ends feature a curved tip profile. The appropriate end type depends on the screw specification and intended application.
Dimension Chart:
| Thread size | ST 1,5 | ST 1,9 | ST 2,2 | ST 2,6 | ST 2,9 | ST 3,3 | ST 3,5 | ST 3,9 | ST 4,2 | ST 4,8 | ST 5,5 | ST 6,3 | ST 8 | ST 9,5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P ≈ | 0,5 | 0,6 | 0,8 | 0,9 | 1,1 | 1,3 | 1,3 | 1,3 | 1,4 | 1,6 | 1,8 | 1,8 | 2,1 | 2,1 |
| d₁ max. | 1,52 | 1,90 | 2,24 | 2,57 | 2,90 | 3,30 | 3,53 | 3,91 | 4,22 | 4,80 | 5,46 | 6,25 | 8,00 | 9,65 |
| d₁ min. | 1,38 | 1,76 | 2,10 | 2,43 | 2,76 | 3,12 | 3,35 | 3,73 | 4,04 | 4,62 | 5,28 | 6,03 | 7,78 | 9,43 |
| d₂ max. | 0,91 | 1,24 | 1,63 | 1,90 | 2,18 | 2,39 | 2,64 | 2,92 | 3,10 | 3,58 | 4,17 | 4,88 | 6,20 | 7,85 |
| d₂ min. | 0,84 | 1,17 | 1,52 | 1,80 | 2,08 | 2,29 | 2,51 | 2,77 | 2,95 | 3,43 | 3,99 | 4,70 | 5,99 | 7,59 |
| d₃ max. | 0,79 | 1,12 | 1,47 | 1,73 | 2,01 | 2,21 | 2,41 | 2,67 | 2,84 | 3,30 | 3,86 | 4,55 | 5,84 | 7,44 |
| d₃ min. | 0,69 | 1,02 | 1,37 | 1,60 | 1,88 | 2,08 | 2,26 | 2,51 | 2,69 | 3,12 | 3,68 | 4,34 | 5,64 | 7,24 |
| c max. | 0,1 | 0,1 | 0,1 | 0,1 | 0,1 | 0,1 | 0,1 | 0,1 | 0,1 | 0,15 | 0,15 | 0,15 | 0,15 | 0,15 |
| rᵃ ≈ | — | — | — | — | — | — | 0,5 | 0,6 | 0,6 | 0,7 | 0,8 | 0,9 | 1,1 | 1,4 |
| y ref.ᵇ Type C | 1,4 | 1,6 | 2 | 2,3 | 2,6 | 3 | 3,2 | 3,5 | 3,7 | 4,3 | 5 | 6 | 7,5 | 8 |
| y ref.ᵇ Type F | 1,1 | 1,2 | 1,6 | 1,8 | 2,1 | 2,5 | 2,5 | 2,7 | 2,8 | 3,2 | 3,6 | 3,6 | 4,2 | 4,2 |
| y ref.ᵇ Type R | — | — | — | — | — | — | 2,7 | 3 | 3,2 | 3,6 | 4,3 | 5 | 6,3 | — |
| Numberᶜ | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 10 | 12 | 14 | 16 | 20 |
| a: Dimension r is a reference and has been provided for guidance only. b:The end may not be perfectly spherical but shall not be sharp to the touch. b Length of incomplete thread. C Former thread designation, for information only. | ||||||||||||||